Best artist or book, depends on what you like and what your skill level is. the list of excellent creators gets longer every day, but below are a few names recognized for different things from animals, modulars, complex folding, and tessellations.

Some are important parts of the history of origami and have passed away (like Yoshizawa, Neil Elias, Eric Joisel) others have been around for years (Lang Montroll). There are more names of great authors than could be put in a list and many of them post here in these forums, so i hope no one is offended for not being mentioned. There are free models online from almost all of these authors that you can test out

One book i always recommend because it is reasonably priced and has models across a range of skill levels is: Genuine Origami by Jun Maekawa

Another rather unknown but very good designer is Yoshino Issei.sadly, he died in late 1996, but his models still are very good, some even better than what you would find today. He was the Satoshi Kamiya of the '90s.

They're not being killed off; as far as I know they all died naturally. Kamiya is pretty young, but I guess a few folders out there are getting pretty old (Lang's in his mid-60s, I think). But hopefully they'll still be around for several more years.